α-olefins are useful intermediates in preparing diesel and jet/turbine fuels. They are also use in preparing poly-α-olefins (PAOs) and copolymers with ethylene to form low density plastics. If the α-olefins are made from petroleum resources, then there exist several well known processes for ethylene oligomerization that afford α-olefins such as 1-butene, 1-hexene, 1-octene, and so forth, and after a distillation and purification process can yield a single pure terminal olefin. The Shell SHOP process is perhaps the best known to those skilled in the art of ethylene oligomerization.
Obtaining α-olefins made from renewable and sustainable resources requires quite a different approach. Since alcohols can be produced in large scale by fermentation processes, they can be viewed as an attractive feedstock for α-olefins provided that they can be dehydrated in high yield and with high regioselectivity. Particular to α-olefins is a distinct and thermodynamically driven isomerization reaction to the more stable internal-olefin. For example, dehydration of 1-butanol often produces a mixture of 1-butene and 2-butene where the latter is a result of 1-butene isomerizing to the more thermodynamically stable 2-butene. It is well known this type of double-bond isomerization is facilitated by acid catalysts; hence, to maintain 1-butene as the dominant product, a successful process must avoid interaction with acidic catalyst sites.
Bio-1-butanol in particular has a rich history of success and large scale commercial production since the discovery by Louis Pasteur in 1862 where he first revealed bacteria that could ferment sugars to a mixture of acetone, 1-butanol, and ethanol (ABE). Since Pasteur's initial discovery of the ABE process many advances have been made in the fermentation process to optimize bio-1-butanol production and reduce ethanol and acetone co-production. Most notably are the successful efforts using non-engineered bacteria that in fact have led to commercial plants operating for decades that produce bio-1-butanol.
Since fermentations are carried out in water, separation of the fermentation products from the water and bacteria “soup” is energy and time intensive. In the case of bio-1-butanol, several methods have been reported for isolating the alcohol component. One method that has found commercial success is use of a sparging gas (e.g. carbon dioxide or steam) that carries the more volatile bio-1-butanol/water azeotrope away from the fermentation broth. Other more academic approaches involve pervaporization. In this case, a selective-membrane material is used that permits bio-1-butanol pass through, thus leaving the bacteria and water behind. Regardless of the method it is evident to those skilled in the art that removing the last traces of impurities and water are costly in energy and time. The methods vary significantly in capabilities. However, water and impurities are a direct and unavoidable consequence from bioalcohol fermentation processing. Ruwet et al. (Bull. Soc. Chim. 1987, 96, 281-292) discuss the problems in using a wet ABE bio-1-butanol feed in a dehydration reaction to afford a mixture of olefins. More recently, D'amore et al. (patent appl. US 2008/0015395 A1) showed extreme difficulty in dehydrating aqueous solutions of 1-butanol using a variety of acid catalysts to afford a mixture of olefins and other oxygenated products (e.g. ethers) coupled to high amounts of unreacted 1-butanol. There is clearly no obvious and proficient method for preparing terminal bio-1-olefins efficiently from bio-1-alcohols that contain water as a major impurity.